Device for detecting malfunction of fuel evaporative purge system

Abstract

A device for detecting a malfunction of a fuel evaporative purge system comprises a temperature sensor for detecting a temperature inside a canister. During the absorbing and purging operations of the purge system, the device calculates changes in the temperature when absorbing and purging and compares the temperature changes with predetermined values denoting that the purge system is operating normally, and determines whether a malfunction has occurred in the purge system from the result of the comparison.

We claim: 
     
       1. A device for detecting a malfunction of a fuel evaporative purge system having a canister for absorbing fuel vapor caused by an evaporation of fuel held in a fuel tank, said purge system absorbing the fuel vapor at least when a vehicle is stopped, and purging the fuel vapor held in said canister to an engine of said vehicle when said vehicle is running, said device comprising: means for detecting a temperature inside said canister;   means for calculating a change of said temperature when absorbing the fuel vapor and a change of said temperature when purging the fuel vapor   means for determining whether or not a malfunction has occurred in said system by comparing said changes of temperature calculated by said calculating means with predetermined values.   
     
     
       2. A device according to claim 1, wherein said fuel evaporative purge system comprises a refuelling switch arranged at a fuel inlet of said fuel tank and activated when said fuel tank is replenished with fuel, and a valve arranged at a vapor inlet of a vapor passage connecting said fuel tank with said canister and opened when said refuelling switch is activated, whereby said purge system absorbs the fuel vapor when the vehicle is stopped and the fuel is replenished. 
     
     
       3. A device according to claim 2, wherein said fuel evaporative purge system further comprises a solenoid valve arranged in a purge passage connecting said canister with an intake pipe of said engine and opened when the vehicle is running, whereby said purge system purges the fuel vapor from said canister to said intake pipe when the vehicle is running. 
     
     
       4. A device according to claim 3, wherein said solenoid valve is opened when a speed of the vehicle is higher than a predetermined value. 
     
     
       5. A device according to any one of the preceding claims, wherein said detecting means comprises a temperature sensor inserted into said canister. 
     
     
       6. A device according to claim 5, wherein said calculating means calculates a difference between a maximum temperature of said temperature detected when the vehicle is stopped and said temperature detected just before the vehicle is stopped, and another difference between said maximum temperature and a minimum temperature among temperatures detected within a predetermined interval after the vehicle is run. 
     
     
       7. A device according to claim 6, wherein said determining means determines that a malfunction has occurred in said purge system when at least one of said calculated differences is lower than said corresponding predetermined value. 
     
     
       8. A device according to claim 7, wherein said determining means includes a warning lamp which is activated when a malfunction has occurred in said purge system. 
     
     
       9. A device according to claim 8, wherein said warning lamp is turned ON and OFF to display a code corresponding to the kind of malfunction that has occurred in said purge system. 
     
     
       10. A device according to claim 9, wherein said canister contains an activated carbon. 
     
     
       11. A device according to claim 10, wherein said canister is provided with a filter which cleans fresh air introduced thereinto, and plates support therebetween said filter.